Magnetic memory structure and method of forming the same

ABSTRACT

The present disclosure provides a semiconductor structure, including an N th  metal layer over a transistor region, where N is a natural number, and a bottom electrode over the N th  metal layer. The bottom electrode comprises a bottom portion having a first width, disposed in a bottom electrode via (BEVA), the first width being measured at a top surface of the BEVA, and an upper portion having a second width, disposed over the bottom portion. The semiconductor structure also includes a magnetic tunneling junction (MTJ) layer having a third width, disposed over the upper portion, a top electrode over the MTJ layer and an (N+1) th  metal layer over the top electrode. The first width is greater than the third width.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a divisional application of U.S. patent applicationSer. No. 15/159,669, filed May 19, 2016, entitled “SEMICONDUCTORSTRUCTURE AND METHOD OF FORMING THE SAME,” which claims priority to U.S.provisional patent application Ser. No. 62/273,469 filed Dec. 31, 2015,the disclosures of each are hereby incorporated by reference in theirentirety.

BACKGROUND

Semiconductors are used in integrated circuits for electronicapplications, including radios, televisions, cell phones, and personalcomputing devices. One type of well-known semiconductor device is thesemiconductor storage device, such as dynamic random access memories(DRAMs), or flash memories, both of which use charges to storeinformation.

A more recent development in semiconductor memory devices involves spinelectronics, which combines semiconductor technology and magneticmaterials and devices. The spin polarization of electrons, rather thanthe charge of the electrons, is used to indicate the state of “1” or“0.” One such spin electronic device is a spin torque transfer (STT)magnetic tunneling junction (MTJ) device

MTJ device includes free layer, tunnel layer, and pinned layer. Themagnetization direction of free layer can be reversed by applying acurrent through tunnel layer, which causes the injected polarizedelectrons within free layer to exert so-called spin torques on themagnetization of free layer. Pinned layer has a fixed magnetizationdirection. When current flows in the direction from free layer to pinnedlayer, electrons flow in a reverse direction, that is, from pinned layerto free layer. The electrons are polarized to the same magnetizationdirection of pinned layer after passing pinned layer; flowing throughtunnel layer; and then into and accumulating in free layer. Eventually,the magnetization of free layer is parallel to that of pinned layer, andMTJ device will be at a low resistance state. The electron injectioncaused by current is referred to as a major injection.

When current flowing from pinned layer to free layer is applied,electrons flow in the direction from free layer to pinned layer. Theelectrons having the same polarization as the magnetization direction ofpinned layer are able to flow through tunnel layer and into pinnedlayer. Conversely, electrons with polarization differing from themagnetization of pinned layer will be reflected (blocked) by pinnedlayer and will accumulate in free layer. Eventually, magnetization offree layer becomes anti-parallel to that of pinned layer, and MTJ devicewill be at a high resistance state. The respective electron injectioncaused by current is referred to as a minor injection.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1A is a cross section of a semiconductor structure, in accordancewith some embodiments of the present disclosure.

FIG. 1B is a cross section of a semiconductor structure, in accordancewith some embodiments of the present disclosure.

FIG. 2 is a cross section of a semiconductor structure, in accordancewith some embodiments of the present disclosure.

FIG. 3 to FIG. 23 are cross sections of a CMOS-MEMS structure fabricatedat various stages, in accordance with some embodiments of the presentdisclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the disclosure are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard deviation found in therespective testing measurements. Also, as used herein, the term “about”generally means within 10%, 5%, 1%, or 0.5% of a given value or range.Alternatively, the term “about” means within an acceptable standarderror of the mean when considered by one of ordinary skill in the art.Other than in the operating/working examples, or unless otherwiseexpressly specified, all of the numerical ranges, amounts, values andpercentages such as those for quantities of materials, durations oftimes, temperatures, operating conditions, ratios of amounts, and thelikes thereof disclosed herein should be understood as modified in allinstances by the term “about.” Accordingly, unless indicated to thecontrary, the numerical parameters set forth in the present disclosureand attached claims are approximations that can vary as desired. At thevery least, each numerical parameter should at least be construed inlight of the number of reported significant digits and by applyingordinary rounding techniques. Ranges can be expressed herein as from oneendpoint to another endpoint or between two endpoints. All rangesdisclosed herein are inclusive of the endpoints, unless specifiedotherwise.

Embedded MRAM cell in a CMOS structure has been continuously developed.A semiconductor circuit with embedded MRAM cell includes an MRAM cellregion and a logic region separated from the MRAM cell region. Forexample, the MRAM cell region may locate at the center of the aforesaidsemiconductor circuit while the logic region may locate at a peripheryof the semiconductor circuit. Note the previous statement is notintended to be limiting. Other arrangement regarding the MRAM cellregion and the logic region are enclosed in the contemplated scope ofthe present disclosure.

In the MRAM cell region, a transistor structure can be disposed underthe MRAM structure. In some embodiments, the MRAM cell is embedded inthe metallization layer prepared in a back-end-of-line (BEOL) operation.For example, the transistor structures in the MRAM cell region and inthe logic region are disposed in a common semiconductor substrate,prepared in a front-end-of-line operation, and are substantiallyidentical in the aforesaid two regions in some embodiments. The MRAMcell can be embedded in any position of the metallization layer, forexample, between adjacent metal line layers distributed horizontallyparallel to a surface of the semiconductor substrate. For instance, theembedded MRAM can be located between the 4^(th) metal line layer and the5^(th) metal line layer in an MRAM cell region. Horizontally shifted tothe logic region, the 4^(th) metal line layer is connected to the 5^(th)metal line layer though a 4^(th) metal via. In other words, taking theMRAM cell region and the logic region into consideration, the embeddedMRAM occupies a thickness of at least a portion of the 5^(th) metal linelayer and the 4^(th) metal via. The number provided for the metal linelayer herein is not limiting. In general, people having ordinary skillin the art can understand that the MRAM is located between an N^(th)metal line layer and an (N+1)^(th) metal line layer, where N is anatural number.

The embedded MRAM includes a magnetic tunneling junction (MTJ) composedof ferromagnetic materials. A bottom electrode and a top electrode areelectrically coupled to the MTJ for signal/bias conveyance. Followingthe example previously provided, the bottom electrode is furtherconnected to the N^(th) metal line layer, whereas the top electrode isfurther connected to the (N+1)^(th) metal line layer. The remainingspaces are filled with dielectric layers for protection and electricalinsulation between N^(th) metal line layer and the (N+1)^(th) metal linelayer. In some embodiments, the dielectric layers may include materialsdifferent from those in the top electrode, the MTJ, the bottomelectrode, and metal in the metal line layer in order to achieve desiredfeature geometry and insulating performance.

There is, however, excessive loss of the dielectric layers surroundingthe bottom electrode and in proximity to the N^(th) metal line. Forexample, the etchant used for defining the top electrode, the MTJ layerand the bottom electrode is non-selective to any of the aforesaid layersand may over-etch the underlying dielectric layers. Result of noselectivity between the bottom electrode and the underlying dielectriclayers may cause the N^(th) metal line below the dielectric layers to beexposed or excessively thinned. This damage applies to both the MRAMcell region and the logic region. Thus, the damage to the dielectriclayer leads to the underlying metal, for example, Cu atom, migration andhenceforth the occurrence of short circuit in both the MRAM cell regionand the logic region.

Furthermore, in the process of forming the MTJ, a suitable removingprocess, such as dry etching, is adopted subsequent to a depositionprocess of the MTJ stack such that the MTJ is patterned. During the dryetching process, particles are scattered due to bombarding the bottomelectrode material. Those scattered particles may be sputtered back toneighboring features, such as the sidewall of the as-patterned MTJ, andlead to short circuit or current leakage.

The present disclosure provides a semiconductor structure where thebottom electrode has a greater width than that of a bottom of the MTJ ora bottom of the top electrode. In addition, the MRAM may include aspacer disposed on the bottom electrode. Thus, the etching operation ofthe bottom electrode is separated from the etching operation of the topelectrode and the MTJ by a spacer formation operation. The operationintroduced in the present disclosure prevents the dielectric layerssurrounding the bottom electrode via from being damaged and effectivelyreduce the chance of migration of underlying metal atoms.

Referring to FIG. 1A, FIG. 1A is a cross section of a semiconductorstructure 10, in accordance with some embodiments of the presentdisclosure. The semiconductor structure 10 can be a semiconductorcircuit including a MRAM cell region 100A. In some embodiments, thesemiconductor structure 10 may include other regions. The MRAM cellregion 100A has a transistor structure 101 in a semiconductor substrate100. In some embodiments, the semiconductor substrate 100 may be but isnot limited to, for example, a silicon substrate. In one embodiment,substrate 100 may include other semiconductor materials, such as silicongermanium, silicon carbide, gallium arsenide, or the like. In thepresent embodiment, the semiconductor substrate 100 is a p-typesemiconductor substrate (P-Substrate) or an n-type semiconductorsubstrate (N-Substrate) comprising silicon. Alternatively, the substrate100 includes another elementary semiconductor, such as germanium; acompound semiconductor including silicon carbide, gallium arsenic,gallium phosphide, indium phosphide, indium arsenide, and/or indiumantimonide; an alloy semiconductor including SiGe, GaAsP, AlInAs,AlGaAs, GaInAs, GaInP, and/or GaInAsP; or combinations thereof. In yetanother alternative, the semiconductor substrate 100 is a semiconductoron insulator (SOI). In other alternatives, semiconductor substrate 100may include a doped epi layer, a gradient semiconductor layer, and/or asemiconductor layer overlying another semiconductor layer of a differenttype, such as a silicon layer on a silicon germanium layer. Thesemiconductor substrate 100 may or may not include doped regions, suchas a p-well, an n-well, or combination thereof.

The semiconductor substrate 100 further includes heavily doped regionssuch as sources 103 and drains 105 at least partially in thesemiconductor substrate 100. A gate 107 is positioned over a top surfaceof the semiconductor substrate 100 and between the source 103 and thedrain 107. Contact plugs 108 are formed in inter-layer dielectric (ILD)109, and may be electrically coupled to the transistor structure 101. Insome embodiments, the ILD 109 is formed on the semiconductor substrate100. The ILD 109 may be formed by a variety of techniques for formingsuch layers, e.g., chemical vapor deposition (CVD), low-pressure CVD(LPCVD), plasma-enhanced CVD (PECVD), sputtering and physical vapordeposition (PVD), thermal growing, and the like. The ILD 109 above thesemiconductor substrate 100 may be formed from a variety of dielectricmaterials and may, for example, be an oxide (e.g., Ge oxide), anoxynitride (e.g., GaP oxynitride), silicon dioxide (SiO₂), anitrogen-bearing oxide (e.g., nitrogen-bearing SiO₂), a nitrogen-dopedoxide (e.g., N₂-implanted SiO₂), silicon oxynitride (SiO_(y)N_(z)), andthe like.

FIG. 1A shows a planar transistor having a doped region in thesemiconductor substrate 100. However, the present disclosure is notlimited thereto. Any non-planar transistor, such as a FinFET structure,can have raised doped regions.

In some embodiments, a shallow trench isolation (STI) 111 is provided todefine and electrically isolate adjacent transistors. A number of STI111 are formed in the semiconductor substrate 100. The STI 111, whichmay be formed of suitable dielectric materials, may be provided toisolate a transistor electrically from neighboring semiconductor devicessuch as other transistors. The STI 111 may, for example, include anoxide (e.g., Ge oxide), an oxynitride (e.g., GaP oxynitride), silicondioxide (SiO₂), a nitrogen-bearing oxide (e.g., nitrogen-bearing SiO₂),a nitrogen-doped oxide (e.g., N₂-implanted SiO₂), silicon oxynitride(Si_(x)O_(y)N_(z)), and the like. The STI 111 may also be formed of anysuitable “high dielectric constant” or “high K” material, where K isgreater than or equal to about 8, such as titanium oxide (Ti_(x)O_(y),e.g., TiO₂), tantalum oxide (Ta_(x)O_(y), e.g., Ta₂O₅), barium strontiumtitanate (BST, BaTiO₃/SrTiO₃), and the like. Alternatively, the STI 111may also be formed of any suitable “low dielectric constant” or “low K”dielectric material, where K is less than or equal to about 4.

Referring to FIG. 1A, a metallization structure 101′ is disposed abovethe transistor structure 101. Because the N^(th) metal layer 121′ maynot be the first metal layer over the transistor structure 101, theomission of a portion of the metallization structure 101′ is representedby dots. In the MRAM cell region 100A, an MTJ structure 130 is disposedbetween an N^(th) metal line 121′ of the N^(th) metal layer 121 and an(N+1)^(th) metal line 123′ of the (N+1)^(th) metal layer 123. In someembodiments, the metal lines are filled with electrically conductivematerial, e.g. copper, gold or another suitable metal or alloy, to forma number of conductive vias. Metal lines in different metal layers forman interconnect structure composed of substantially pure copper (forexample, with a weight percentage of copper being greater than about 90percent, or greater than about 95 percent) or copper alloys, and may beformed using the single and/or dual damascene processes. Theinterconnect structure may further include metal vias 122 connectingmetal lines 123′ in the metal layers. Metal vias are filled withelectrically conductive material similar to metal lines. In addition,metal lines and metal vias may be, or may not be, substantially freefrom aluminum. Interconnect structure includes a plurality of metallayers, namely M₁, M₂ . . . M_(N). Throughout the description, the term“metal layer” refers to the collection of the metal lines in the samelayer. Metal layers M₁ through M_(N) are formed in inter-metaldielectrics (IMDs) 125, which may be formed of oxides such as un-dopedSilicate Glass (USG), Fluorinated Silicate Glass (FSG), low-k dielectricmaterials, or the like. The low-k dielectric materials may have k valueslower than 3.8, although the dielectric materials of IMDs 125 may alsobe close to 3.8. In some embodiments, the k values of the low-kdielectric materials are lower than about 3.0, and may be lower thanabout 2.5. The via 122 may be formed by a variety of techniques, e.g.,electroplating, electroless plating, high-density ionized metal plasma(IMP) deposition, high-density inductively coupled plasma (ICP)deposition, sputtering, physical vapor deposition (PVD), chemical vapordeposition (CVD), low-pressure chemical vapor deposition (LPCVD),plasma-enhanced chemical vapor deposition (PECVD), and the like.

Referring to the MRAM cell region 100A of the semiconductor structure10, the MTJ structure 130 at least includes a bottom electrode 137, atop electrode 133, and an MTJ 135. In some embodiments, the bottomelectrode 137 possesses a trapezoidal recess surrounded by a compositedielectric layer including SiC 141 and tetraethyl orthosilicate (TEOS)142, for example. Alternatively, the TEOS 142 can be replaced orcombined with silicon-rich oxides (SRO). In some embodiments, the bottomelectrode 137 may include nitrides such as TiN, TaN or Ta. In someembodiments, the bottom electrode 137 is formed of stacked sublayerswhere each sublayer may have a different width. Details of the stackedsublayers of the bottom electrode 137 are further described in thefollowing paragraphs associated with FIG. 2.

In some embodiments as shown in the MRAM cell region 100A of FIG. 1A,the (N+1)^(th) metal line 123′ is surrounded by SiC 141 in addition tothe IMDs 125. As shown in FIG. 1A, sidewalls of the top electrode 133and the MTJ 135 is laterally surrounded by a spacer 143 composed of, forexample, nitrides, oxides, or oxynitrides. In some embodiments, a topsurface of the bottom electrode 137 is wider than that at a bottomsurface of the top electrode 133 and that at a bottom surface of the MTJ135 such that the spacer 143 is disposed only on a periphery of thebottom electrode 137. In some embodiments, MTJ 135 and the top electrode133 are designed to have a predetermined pattern (e.g., a circularshape) from a top view perspective, and the spacer 143 laterallysurrounds the sidewall of the MTJ 135 and the top electrode 133. In someembodiments, the side of the spacer 143 away from the MTJ 135 is alignedwith a boundary of the bottom electrode 137. In some embodiments, thespacer 143 may be formed in a multi-layer structure. For example, afirst spacer material is disposed on the MTJ structure 130 and a secondspacer material is formed over the first spacer material. The firstspacer material may be different from the second spacer material.

In some embodiments, the spacer 143 is laterally surrounded by aprotection layer 127 such as a nitride layer. In some embodiments, theprotection layer 127 is optional and can include silicon nitrides. Insome embodiments, a dielectric layer 129 can be disposed over theprotection layer 127. In some embodiments, a TEOS layer 142 can bedisposed over the SiC 141, surrounding the (N+1)^(th) metal line 123′.

In some embodiments, the bottom electrode 137 of the MTJ structure 130is electrically coupled with the doped region. In some embodiments, thedoped region is a drain 105 or a source 103. In other embodiments, thebottom electrode 137 of the MTJ structure 130 is electrically coupledwith the gate 107. In some embodiments, the gate 107 of thesemiconductor structure 10 can be a polysilicon gate or a metal gate.

FIG. 1B is a cross section of a semiconductor structure 20, inaccordance with some embodiments of the present disclosure. Identicalnumeral labels in FIG. 1B are referred to identical elements orequivalents thereof as shown in FIG. 1A and are not repeated here forsimplicity. A difference between the semiconductor structure 20 from thesemiconductor structure 10 lies in that, in addition to the MRAM cellregion 100A, the semiconductor structure 20 further includes a logicregion 100B. Similar to the MRAM region 100A, the logic region 100B hascommon transistor structure 101 in the semiconductor substrate 100. Inthe logic region 100B, the N^(th) metal line 121′ is connected to the(N+1)^(th) metal line 123′ by an N^(th) metal via 122′ of the N^(th)metal layer 121. Moreover, comparing the MRAM cell region 100A and thelogic region 100B1, the (N+1)^(th) metal line 123′ and the N^(th) metalvia 122′ in the logic region 100B is surrounded by the IMDs 125 only. Inaddition, a thickness of the MTJ structure 130 is substantially equal toor greater than a sum of the thickness T2 of the N^(th) metal via 122′and the thickness T1 of a portion of (N+1)^(th) metal line 123′.

FIG. 2 is an enlarged cross section of the semiconductor structure 10 ofFIG. 1A, in accordance with some embodiments of the present disclosure.Referring to FIG. 1A and FIG. 2, the bottom electrode 137 includes astacked structure comprising a bottom portion 131 and an upper portion(top portion) 132. The bottom portion 131 is disposed over andelectrically coupled to the N^(th) metal layer, and the upper portion132 is electrically coupled to the MTJ 135. The bottom portion 131 isdisposed in a bottom electrode via (BEVA) surrounded by the compositelayer 141/142. In some embodiments, a portion of the BEVA is alsosurrounded by the N^(th) metal layer 121. In addition, the bottomportion 131 has a top surface 131A substantially coplanar with the uppersurface of one of the composite layer 142, for example, a TEOS layer. Insome embodiments, the top surface 131A of the bottom portion 131 has aconcave shape which can be resulted from the dishing effect in aplanarization process, such as a chemical mechanical polishing (CMP)operation, for removing the bottom portion 131 excessively formed overthe composite layer 141/142. In some embodiments, the top surface 131Aof the bottom portion 131 possesses a width D4. In some embodiments, abarrier layer 161 is optionally formed on sidewalls and the bottom ofthe BEVA in order to prevent Cu diffusion and provide better adhesionbetween the bottom electrode 137 and its neighboring layers.

The upper portion 132 of the bottom electrode 137 has a bottom surface132B contacting the top surface 131A of the bottom portion 131. Theupper portion 132 possesses a width D3. In some embodiments, the widthD3 is uniform from the center to the edge of the upper portion 132regardless of measuring from a top surface or a bottom surface of theupper portion 132. The top electrode 133 has a bottom surface having awidth D1. The MTJ 135 has a bottom surface having a, width D2.Consequently, the width D3 is greater than the width D4. Moreover, thewidth D3 is greater than the width D1 and the width D2. Referring toFIG. 2, the spacer 143 laterally surrounds the MTJ 135 and the topelectrode 133 from sidewalls thereof and forms a hollow cylinder featureviewing from a top view perspective. Therefore, a thickness D32 of thespacer 143 can be measured along the top surface 132A of the upperportion 132. Alternatively stated, the thickness D32 is a thickestportion between one side 143A and the other side 143B of the spacer 143.Thus, the width D3 is substantially equal to summation of the width D2at the bottom surface of the MTJ 135 and two widths D32 situated at bothsides of the MTJ 135 and the top electrode 133. In some embodiments, thethickness D32 is from about 5 nm to about 25 nm. In some embodiments,the width D3 is greater than the width D2 by a range of from 10 nm to 50nm. In addition, the upper portion 132 has a thickness of T3.

FIG. 3 to FIG. 23 are cross sections of a CMOS-MEMS structure fabricatedat various stages, in accordance with some embodiments of the presentdisclosure. In FIG. 3, a semiconductor structure having a predeterminedMRAM cell region 100A and a logic region 100B is provided. In someembodiments, a transistor structure is pre-formed in a semiconductorsubstrate (not shown in FIG. 3). The integrated circuit device mayundergo further CMOS or MOS technology processing to form variousfeatures known in the art. For example, one or more contact plugs, suchas silicide regions, may also be formed. The contact features may becoupled to the source and drain. The contact features comprise silicidematerials, such as nickel silicide (NiSi), nickel-platinum silicide(NiPtSi), nickel-platinum-germanium silicide (NiPtGeSi),nickel-germanium silicide (NiGeSi), ytterbium silicide (YbSi), platinumsilicide (PtSi), iridium silicide (IrSi), erbium silicide (ErSi), cobaltsilicide (CoSi), other suitable conductive materials, and/orcombinations thereof. In an example, the contact features are formed bya salicide (self-aligned silicide) process.

An N^(th) metal line 121′ is patterned in a dielectric layer 128 overthe transistor structure. In some embodiments, the N^(th) metal line121′ can be formed of an electroplating operation with a Cu seed layerdeposited over the patterned dielectric layer 128. In other embodiments,the N^(th) metal line 121′ may be formed by a variety of techniques,e.g., electroless plating, high-density ionized metal plasma (IMP)deposition, high-density inductively coupled plasma (ICP) deposition,sputtering, physical vapor deposition (PVD), chemical vapor deposition(CVD), low-pressure chemical vapor deposition (LPCVD), plasma-enhancedchemical vapor deposition (PECVD), and the like. A planarizationoperation is performed to expose a top surface of the N^(th) metal line121′ and the top surface of the dielectric layer 128.

In FIG. 4, a, barrier layer 140 in a form of a, stacking layer includinga SiC layer 141 and a TEOS/SRO layer 142 are blanket deposited over atop surface of the N^(th) metal line 121′ and a top surface of thedielectric layer 128, in both the MRAM cell region 100A and the logicregion 100B. The barrier layer 140 can be formed by a variety oftechniques, e.g., chemical vapor deposition (CVD), low-pressure CVD(LPCVD), plasma-enhanced CVD (PECVD), sputtering and physical vapordeposition (PVD), thermal growing, and the like. In FIG. 5, aphotoresist layer (not shown) is patterned over the stacking layer toexpose a bottom electrode region of the MTJ structure. As shown in FIG.5, a bottom electrode via hole 137′ is formed in the barrier layer 140by a, suitable dry etch operation. In some embodiments, the dry etch inthe present operation includes reactive ion etch (RIE) adoptingfluorine-containing gases. In some embodiments, the present dry etchoperation can be any suitable dielectric etch to form via trenches in ametallization structure of conventional CMOS technology. Referring tothe logic region 100B as shown in FIG. 5, the barrier layer 140 isprotected by the photoresist layer (not shown) such that a top surfaceof the N^(th) metal layer 121′ is not exposed as opposed to thecounterpart in the MRAM cell region 100A.

In FIG. 6, a diffusion barrier layer 161 is blanket lined over thebottom electrode via hole 137′ in the MRAM cell region 100A and over thebarrier layer 140 in the logic region 100B. Subsequently, a bottomportion material 131 is conducted to be disposed over the diffusionbarrier layer 161 and the barrier layer 140. The bottom portion material131 may be formed by a variety of techniques, e.g., high-density ionizedmetal plasma (IMP) deposition, high-density inductively coupled plasma(ICP) deposition, sputtering, physical vapor deposition (PVD), chemicalvapor deposition (CVD), low-pressure chemical vapor deposition (LPCVD),plasma-enhanced chemical vapor deposition (PECVD), and the like. Thediffusion barrier layer 161 and the bottom portion material 131 is thenetched back to level with a top surface of the barrier layer 140, asillustrated in FIG. 7. In some embodiments, the etch back operationincludes a CMP operation. As discussed above, if the opening of thebottom electrode via hole 137′ is wider than a predetermined value, adishing effect occurs in the bottom portion material 131 as a result ofCMP operation. In FIG. 8, an upper portion material 132 is blanketformed over the planarized bottom portion material 131 and the barrierlayer 140. The deposited upper portion material 132 may be formed by a,variety of techniques, e.g., high-density ionized metal plasma (IMP)deposition, high-density inductively coupled plasma (ICP) deposition,sputtering, physical vapor deposition (PVD), chemical vapor deposition(CVD), low-pressure chemical vapor deposition (LPCVD), plasma-enhancedchemical vapor deposition (PECVD), and the like. The upper portionmaterial 132 is then thinned to a predetermined thickness T3, asillustrated in FIG. 9. In some embodiments, the thickness T3 is fromabout 80 Å to about 300 Å. The bottom portion material 131 and the upperportion material 132 can be composed of metal nitride such as TaN, TiN,Ti/TiN, TaN/TiN, Ta or the combinations thereof. In some embodiments,the upper portion 132 has a material different from a material of thebottom portion 131. The bottom portion material 131 and the upperportion material 132 are collectively referred to as the bottomelectrode 137.

FIG. 10 shows the formation of the MTJ 135 and the top electrode 133 ofan MTJ structure 130. In FIG. 10, the MTJ 135 is deposited in a form ofmultiple material stacks over the bottom electrode 137. In someembodiments, the MTJ 135 is having a thickness of from about 150 Å toabout 250 Å. The MTJ 135 may be formed by variety of techniques, e.g.,high-density ionized metal plasma (IMP) deposition, high-densityinductively coupled plasma (ICP) deposition, sputtering, physical vapordeposition (PVD), chemical vapor deposition (CVD), low-pressure chemicalvapor deposition (LPCVD), plasma-enhanced chemical vapor deposition(PECVD), and the like. In some embodiments, the MTJ 135 may includeferromagnetic layers, MTJ spacers, and a capping layer. The cappinglayer is formed on the ferromagnetic layer. Each of the ferromagneticlayers may include ferromagnetic material, which may be metal or metalalloy, for example, Fe, Co, Ni, CoFeB, FeB, CoFe, FePt, FePd, CoPt,CoPd, CoNi, TbFeCo, CrNi or the like. The MTJ spacer may includenon-ferromagnetic metal, for example, Ag, Au, Cu, Ta, W, Mn, Pt, Pd, V,Cr, Nb, Mo, Tc, Ru or the like. Another MTJ spacer may also includeinsulator, for example, Al₂O₃, MgO, TaO, RuO or the like. The cappinglayer may include non-ferromagnetic material, which may be a metal or aninsulator, for example, Ag, Au, Cu, Ta, W, Mn, Pt, Pd, V, Cr, Nb, Mo,Tc, Ru, Ir, Re, Os, Al₂O₃, MgO, TaO, RuO or the like. The capping layermay reduce write current of its associated MRAM cell. The ferromagneticlayer may function as a, free layer whose magnetic polarity or magneticorientation can be changed during write operation of its associated MRAMcell. The ferromagnetic layers and the MTJ spacer may function as afixed or pinned layer whose magnetic orientation may not be changedduring operation of its associated MRAM cell. It is contemplated thatthe MTJ 135 may include an antiferromagnetic layer in accordance withother embodiments. Following the formation of the MTJ 135, a topelectrode layer 133 is deposited over the MTJ 135. The top electrodelayer 133 may be formed by a variety of techniques, e.g., high-densityionized metal plasma (IMP) deposition, high-density inductively coupledplasma (ICP) deposition, sputtering, physical vapor deposition (PVD),chemical vapor deposition (CVD), low-pressure chemical vapor deposition(LPCVD), plasma-enhanced chemical vapor deposition (PECVD), and thelike. In some embodiments, the top electrode layer 133 is composed ofTiN.

Referring to FIG. 11, a mask layer (not shown) is formed over the topelectrode 133 for the ensuing MTJ structure formation. The mask layermay have a multi-layer structure, which may include, for example, anoxide layer, an advanced patterning film (APF) layer and an oxide layer.Each of the oxide layer, the APF layer, and the oxide layer may beformed by a variety of techniques, e.g., high-density ionized metalplasma (IMP) deposition, high-density inductively coupled plasma (ICP)deposition, sputtering, physical vapor deposition (PVD), chemical vapordeposition (CVD), low-pressure chemical vapor deposition (LPCVD),plasma-enhanced chemical vapor deposition (PECVD), and the like. In someembodiments, the mask layer is configured to pattern the MTJ 135 and thetop electrode 133. For example, a width of the masking region isdetermined according to the desired MTJ diameter. In some embodiments,the MTJ 135 and the top electrode 133 are formed by an RIE to have atrapezoidal shape viewing from a cross section. In the presentembodiment, the etchants used may be selected from Cl₂, BCl₃, HBr,CF₄CHF₃, H₂, N₂, CO, NH₃, Ar, alcohol and Xe, for example, in order toprovide desirable selectivity between the top portion 132 and the MTJ135. For example, the etchant used in the present etching operationconsumes the MTJ 135 substantially faster than the top portion 132 ofthe bottom electrode 130. In some embodiments, the power used for an RIEoperation is from about 50 Watts to about 3000 Watts.

FIGS. 12-13 show formation of the spacer 143 over the MTJ structure 130.Referring to FIG. 12, a dielectric layer 144 is conformally depositedover the top electrode 133, the MTJ 135 and the upper portion 132 of thebottom electrode 137. The dielectric layer 144 may be formed by a,variety of techniques, e.g., high-density ionized metal plasma (IMP)deposition, high-density inductively coupled plasma (ICP) deposition,sputtering, physical vapor deposition (PVD), chemical vapor deposition(CVD), low-pressure chemical vapor deposition (LPCVD), plasma-enhancedchemical vapor deposition (PECVD), and the like. The dielectric layer144 may include materials such as silicon oxide (SiO_(x)), siliconnitride (SiN_(x)), silicon oxynitride (Si_(x)O_(y)N_(z)), aluminum oxide(AlO_(x)) and the like. A deposition thickness D5 of the dielectriclayer 144 is determined which is closely related to the thickness D32 ofthe spacer 143 in FIG. 2.

In FIG. 13, a portion of the dielectric layer 144 on the top electrode133 and on the top portion 132 of the bottom electrode 137 is removed. Atop surface of the top electrode 133 and a portion of the top portion132 of the bottom electrode 137 are exposed such that spacers 143 areformed on the top surface 132A of the upper portion 132A with aremaining thickness D32 measured along the top surface 132A betweenopposite sidewalls 143A and 143B13. Additionally, the spacer 143laterally surrounds the sidewalls of the MTJ 135 and the top electrode133. The removing operation may be a suitable dry etch operation. Insome embodiments, the dry etch operation in the present embodimentincludes reactive ion etch (RIE) adopting fluorine-containing gases. Theetch operation is conducted using a suitable etchant, such as CF₄, CHF₃,CH₂F₂, Ar, N₂, O₂ and He, in order to provide desired etch selectivitybetween the dielectric layer 144 and the top electrode 133 or topportion 132. In some embodiments, the power used for the etchingoperation is from about 20 Watts to about 1500 Watts. The etch isstopped at the top surface 132A of the top portion 132 such that theupper portion 132 substantially remains its original thickness afteretching.

Referring to FIG. 14, a removing operation is performed for patterningthe top portion 132 of the bottom electrode 137. The removing operationmay be a dry etching operation, such as RIE operation. The etchingconditions are determined to supply high selectivity between the topportion material 132 and the material of the composite layer 142 and thespacer 143. For example, the etch gas is selected from Cl₂, BCl₃, HBr,CF₄, CHF₃, N₂, Ar and He, and the power is controlled at from about 50Watts to about 2000 Watts. Thus, a portion of the composite layer 142 isexposed after the removing operation. Since the spacer 143 is relativelyrobust to the etchant, the upper portion 132 positioned under andshielded by the spacer 143 is not consumed by previous etchingoperation. Consequently, as shown in FIG. 2, the upper portion 132 isformed with a width D3 greater than the width D2 of the bottom surfaceof the MTJ 135. Furthermore, the width D3 is greater than the width D1at the bottom surface of the top electrode 133. Also, the width D3 isgreater than the width D4 of the top surface 131A of the bottom portion131 of the bottom electrode 137. In addition, the upper portion 132 isformed with a substantially uniform width D3 from the surface 132A tothe surface 132B. In some embodiments, the width D3 may be greater thanor less than a, width of the BEVA.

In existing approaches for etching 132, a dry etch operation is usedwhich adopts the same etchant for etching MTJ 135. Such dry etchoperation possesses little or no selectivity to the dielectric layer141/142, therefore, the dielectric layer 141/142 can be easily damagedto an extent allowing the underlying Cu atom to out diffuse or directlyexposing the underlying Cu conductive lines. In contrast, the multi-stepetching operations in the present disclosure prevent the dielectriclayer 141/142 surrounding the bottom electrode 137 from being damagedand effectively reduce the chance of migration of underlying Cu atoms,for example.

Additionally, in conventional MRAM devices the bottom portion 131possesses an uneven surface, for example, a concave surface 131A, due tothe dishing effect resulted from a CMP operation. When the overlying topportion 132 of the bottom electrode 137 is thinner than about 80 Å forthe sake of better control the etching operation forming the MTJstructure 130, such uneven surface may cause a bottom of the MTJ 135 tobe uneven as well. The planarity of the MTJ 135 is crucial to theperformance of the MRAM device. Increasing the thickness T3 of the upperportion 132 as shown in FIG. 9 can effective alleviate the uneven bottomsurface of the MTJ 135 but at the expense of controlling the etchingoperation forming the MTJ structure 130. Conventionally, patterning MTJstructure 130 adopts a first etchant formula for the MTJ 135, and asecond etchant formula for the upper portion 132 of the bottom electrode137. The first etchant formula and the second etchant formula aredifferent. Therefore, the thickness T3 of the upper portion 132 isdetermined to be relatively thin, for example, less than 80 Å,preferably 40 Å, in order to better control the etching operation so asto avoid excessive damage made to the neighboring structures such as thedielectric layer 140. The present disclosure adopts the etchant, such asCF₄, CHF₃ and CH₂F₂, having high selectivity to the upper portion 132without consuming neighboring layers. Thus, the removal of upper portion132 can be completed without damaging the neighboring structures such asthe dielectric layer 140. The thickness of the upper portion 132 in thepresent disclosure may be as thick as compensating the uneven surface ofthe bottom portion 131. In some embodiments, thickness T3 of the upperportion 132 may be in a range of from about 80 Å to about 250 Å.

In some embodiments, the spacer 143 is formed as a protecting mask ofthe MTJ 135 and the top electrode 133 with respect to the subsequentetching operations. During the dry etching for patterning the upperportion 132 of the bottom electrode 137, metal particles from the upperportion 132 are scattered due to ion bombardment. With the spacer 143protecting the sidewall of the MTJ 135 and the top electrode 133, andthe sputtered metal particles may be deposited to neighboring features,such as the sidewall of the spacer 134, rather than the sidewall of theas-patterned MTJ 135 or the top electrode 133. Therefore, unintentionalshort circuit or current leakage due to the above redeposition can beeffectively prevented.

In FIG. 15, a protection layer 127 is conformally formed over the MTJ135, the top electrode 133, the spacer 143 and the composite layer141/142. In some embodiments, the protection layer 127 possesses athickness of from about 50 Å to about 300 Å. Note a sidewall of the MTJ135 and the sidewalls of the upper portion 132 and spacer 143 aresurrounded by the protection layer 127 to prevent oxidation or othercontamination. Subsequently, a dielectric layer 129 such as a TEOS layeris conformally deposited over the protection layer 127. In someembodiments, a, thickness of the dielectric layer 129 is to bedetermined according to a level of a top surface thereof relative to thetop surface of the top electrode 133 and the top of the spacer 143. Forexample, a top surface of the dielectric layer 129 at the logic region100B is to be greater than or about equal to a top surface of the topelectrode 133 of an MTJ structure 130. In FIG. 16, a planarizationoperation is performed on the dielectric layer 129 such that the topsurface of the dielectric layer 129 is substantially flat across theMRAM cell region 100A and the logic region 100B. As shown in FIG. 16,the top surface of the top electrode 133 is exposed from the dielectriclayer 129 after the planarization operation.

In FIG. 17 to FIG. 19, an upper portion of the barrier layer 140, theprotection layer 127, and the dielectric layer 129 are removed from thelogic region 100B by an etch back operation, as illustrated in FIG. 17.Hence, the MRAM cell region 100A is in greater height than the logicregion 100B. In FIG. 18, a dielectric layer-low k-dielectric layercomposite 180 is formed to conformally cover the MRAM cell region 100Aand the logic region 100B. A step difference 181 can be observed in FIG.18, therefore, an etch back operation as illustrated in FIG. 19 isperformed to obtain a substantially flat top surface for the followingtrench formation in both the MRAM cell region 100A and the logic region100B. Note a dielectric layer 183 of the dielectric layer-lowk-dielectric layer composite 180 is remained virtually in the logicregion 100B after the aforesaid planarization operation. The dielectriclayer 183 is deliberately kept to act as a protection layer for thesubsequent trench formation. The dielectric layer 183 can prevent theacidic solution from damaging the low k dielectric layer during aphotoresist stripping operation.

In FIG. 20, photoresist (not shown) is patterned over the planarizeddielectric surface to form trenches for metal lines and metal via. Forexample, in the MRAM cell region 100A, a (N+1)^(th) metal line trench123A is formed over the MTJ structure 130, exposing a, top surface ofthe top electrode 133 of the MTJ structure 130, In the logic region100B, an N^(th) metal via trench and an (N+1)^(th) metal line trench(combinatory 123B) is formed over the N^(th) metal line 121′, exposing atop surface of the N^(th) metal line 121′.

In FIG. 21 and FIG. 22, conductive metal fills the metal linetrench/metal via, trench (hereinafter “trenches”) through, for example,a conventional Dual Damascene operation. The patterned trenches arefilled with a conductive material by an electroplating operation, andexcess portions of the conductive material are removed from the surfaceusing a chemical mechanical polishing (CMP) operation, an etchoperation, or combinations thereof. Details of electroplating thetrenches are provided below. (N+1)^(th) metal line 123′ may be formedfrom W, and more preferably from copper (Cu), including AlCu(collectively, Cu). In one embodiment, (N+1)^(th) metal lines 123′ areformed using the Damascene operation, which should be familiar to thosein the art. First, trenches are etched through the low k dielectriclayer. This process can be performed by plasma etch operation, such asan Inductively Coupled Plasma (ICP) etch. A dielectric liner (not shown)then may be deposited on the trenches sidewalls. In embodiments, theliner materials may include silicon oxide (SiO_(x)) or silicon nitride(SiN_(x)), which may be formed by plasma deposition process, such asphysical vapor deposition (PVD) or chemical vapor deposition (CVD)including plasma enhanced chemical vapor deposition (PECVD). Next, aseed layer of Cu is plated in the trenches. Note the seed layer of Cumay be plated over a top surface of the top electrode 133. Then a layerof copper is deposited in the trenches, followed by planarization of thecopper layer, such as by chemical mechanical polishing (CMP), down tothe top surface of a low k dielectric layer. The exposed copper surfaceand dielectric layer can be coplanar.

After the planarization operation removing the overburden of theconductive metal as illustrated in FIG. 22, an (N+1)^(th) metal line123′ in both the MRAM cell region 100A and the logic region 100B, aswell as an N^(th) metal via 122′ in the logic region 100B, are formed.In FIG. 23, a subsequent barrier layer 141 and (N+1)^(th) metal viatrench as well as (N+2)^(th) metal line trench are formed in the low kdielectric layer. Subsequent processing may further include formingvarious contacts/vias/lines and multilayer interconnect features (e.g.,metal layers and interlayer dielectrics) over the substrate, configuredto connect the various features or structures of the integrated circuitdevice. The additional features may provide electrical interconnectionto the device including the formed metal gate structures. For example, amultilayer interconnection includes vertical interconnects, such asconventional vias or contacts, and horizontal interconnects, such asmetal lines. The various interconnection features may implement variousconductive materials including copper, tungsten, and/or silicide. In oneexample a damascene and/or dual damascene process is used to form acopper related multilayer interconnection structure.

Some embodiments of the present disclosure provide a semiconductorstructure, including an N^(th) metal layer over a transistor region,where N is a natural number, and a bottom electrode over the N^(th)metal layer. The bottom electrode comprises a bottom portion having afirst width, disposed in a bottom electrode via (BEVA), the first widthbeing measured at a top surface of the BEVA, and an upper portion havinga second width, disposed over the bottom portion. The semiconductorstructure also includes a magnetic tunneling junction (MTJ) layer havinga third width, disposed over the upper portion, a top electrode over theMTJ layer and an (N+1)^(th) metal layer over the top electrode. Thefirst width is greater than the third width.

Some embodiments of the present disclosure provide a semiconductorstructure including an N^(th) metal layer, a bottom electrode over theNth metal layer, a magnetic tunneling junction (MTJ) layer over thebottom electrode, and a spacer laterally surrounding the MTJ layer. Thebottom electrode comprises a top surface having a first width greaterthan a second width of a bottom surface of the MTJ layer.

Some embodiments of the present disclosure provide a method formanufacturing a semiconductor structure. The method includes (1) formingan N^(th) metal layer, (2) forming a MTJ structure over the Nth metallayer, (3) forming a spacer over the MTJ structure, surrounding asidewall of the MTJ structure, and (4) forming an (N+1)^(th) metal abovethe N^(th) metal.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

What is claimed is:
 1. A method for manufacturing a semiconductorstructure, the method comprising: forming an N^(th) metal layer; forminga MTJ structure over the N^(th) metal layer, wherein the MTJ structurehas a first portion in contact with the N^(th) metal layer and a secondportion over the first portion; forming a spacer over the MTJ structure,surrounding a sidewall of the second portion of the MTJ structure; andforming a (N+1)^(th) metal over the MTJ structure and in contact withthe second portion; wherein a first top surface of the first portion ofthe MTJ structure has a larger width than a first bottom surface of thefirst portion, and wherein a second top surface of the second portion ofthe MTJ structure has a smaller width than a second bottom surface ofthe second portion.
 2. The method of claim 1, wherein the forming theMTJ structure comprises: forming the first portion, the first portionincluding a bottom electrode; forming the second portion over the firstportion, the second portion including a magnetic tunneling junction(MTJ) layer formed over the bottom electrode and a top electrode layerformed over the MTJ layer; and patterning the top electrode layer andthe MTJ layer before the forming the spacer over the MTJ structure. 3.The method of claim 2, wherein the forming the bottom electrode and theforming the spacer over the MTJ structure further comprises: forming abottom electrode layer; and patterning the bottom electrode layer afterthe forming the spacer over the MTJ structure and while the spacer isformed surrounding the sidewall of the second portion of the MTJstructure.
 4. The method of claim 1, further comprising: forming atleast one dielectric layer over the N^(th) metal layer; defining a holein the at least one dielectric layer, wherein the hole exposes aconductive feature of the N^(th) metal layer; and forming a portion ofthe bottom electrode of the MTJ structure in the hole.
 5. The method ofclaim 4, further comprising: forming a conductive layer over the firstportion of the bottom electrode and the at least one dielectric layer.6. The method of claim 5, wherein the forming the MTJ structure over theN^(th) metal layer includes forming a ferromagnetic layer of the MTJstructure on the conductive layer, and wherein the forming the spacerincludes forming the spacer surrounding a sidewall of the ferromagneticlayer and disposed on a second top surface of the conductive layer.
 7. Amethod of fabricating a semiconductor structure, comprising: forming ametal feature of an N^(th) metal layer above a substrate; forming adielectric layer over the N^(th) metal layer; depositing a first portionof a bottom electrode in an opening in the dielectric layer, the firstportion of the bottom electrode connected to the metal feature;depositing a conductive layer over the first portion of the bottomelectrode and the dielectric layer, wherein the conductive layer has asubstantially planar top surface; forming an MTJ element and topelectrode over the conductive layer; forming a spacer on sidewalls ofthe MTJ element and the top electrode, wherein a bottom surface of thespacer interfaces the substantially planar top surface of the conductivelayer; and etching the conductive layer to form a second portion of thebottom electrode, while the spacer is on the sidewalls of the MTJelement and top electrode.
 8. The method of claim 7, wherein the etchingthe conductive layer uses a dry etching process having a selectivitybetween the spacer and the conductive layer.
 9. The method of claim 7,wherein the second portion of the bottom electrode has a greater widththan the MTJ element.
 10. The method of claim 7, further comprising:forming an inter-metal dielectric (IMD) layer over the top electrode;etching a trench in the IMD layer to expose a top surface of the topelectrode; and filling the trench with conductive material to form ametal line of an (N+1)^(th) metal layer.
 11. The method of claim 10,further comprising: etching another trench in the IMD layer in a logicregion of the substrate; and wherein the another trench is coplanar withthe trench and extends to another metal feature of the N^(th) metallayer.
 12. The method of claim 11, wherein the etching the trench andthe etching the another trench in the IMD layer are performed in a sameoperation.
 13. The method of claim 7, further comprising: after theetching the conductive layer, depositing a protection layer and anotherdielectric layer over the top electrode; and planarizing the protectionlayer and the another dielectric layer to expose a top surface of thetop electrode.
 14. A method of fabricating a semiconductor structure,comprising: depositing a first conductive layer over a substrate, thefirst conductive layer having a substantially planar top surface;depositing at least one layer of a magnetic tunneling junction (MTJ)element over a first region of the substantially planar top surface ofthe first conductive layer and depositing a second conductive layer overthe at least one layer of the MTJ element; using a masking element,patterning the at least one layer of the MTJ element and the secondconductive layer to form a patterned MTJ feature; forming a spacer onsidewalls of the patterned MTJ feature and over a second region of thesubstantially planar top surface of the first conductive layer, thesecond region disposed adjacent to and on either side of the firstregion, wherein a bottom surface of the spacer contacts a top surface ofthe substantially planar top surface; and while the spacer is on thesidewalls, selectively etching the first conductive layer outside thefirst and second regions to form a bottom electrode.
 15. The method ofclaim 14, wherein the depositing the at least one layer of the MTJelement includes depositing a ferromagnetic layer, a capping layer, andan insulator layer.
 16. The method of claim 14, wherein patterning formsthe MTJ element having a trapezoidal shape in a cross-section.
 17. Themethod of claim 14, wherein the patterning the at least one layer of theMTJ element and the second conductive layer includes performing anetching of the at least one layer of the MTJ element selective to the atleast one layer of the MTJ element over the first conductive layer. 18.The method of claim 14, further comprising: forming a bottom portion ofthe bottom electrode under the first conductive layer, wherein thebottom portion interfaces a conductive line of a first metal layer. 19.The method of claim 18, further comprising: forming another conductiveline of a second metal layer above and interfacing second conductivelayer of the patterned MTJ feature.
 20. The method of claim 14, whereinafter the selectively etching the first conductive layer to form thebottom electrode, depositing a protection layer over the patterned MTJfeature, wherein the protection layer interfaces sidewalls of the bottomelectrode.